Nicotine is known to have an important role in tobacco dependence. However, in addition to nicotine, smokers are exposed to nornicotine both in the form of a tobacco alkaloid and as a metabolite that results from biotransformation of nicotine. Using an animal model of tobacco smoking in humans, we have found that nornicotine is self-administered in rats and that nornicotine pretreatment is effective in reducing nicotine self-administration. In addition, repeated administration of S(-)-nornicotine, but not R(+)-nornicotine, increases locomotor activity. In the current project, our overall hypothesis is that S(-)-nornicotine will be more potent than R(+)-nornicotine in selectively decreasing nicotine self-administration across repeated injections. The specific aims will determine if the nornicotine enantiomers differ in their ability to (1) dose dependently decrease nicotine self-administration, (2) dose-dependently decrease sucrose-reinforced responding, and (3) decrease nicotine self-administration or sucrose-reinforced responding across repeated injections. Rats will be trained to self-administer nicotine to a stable rate and then will be pretreated with varying doses of either S(-)- or R(+)-nornicotine. To determine the specificity of the decrease in nicotine self- administration, separate groups of rats will be trained to respond for sucrose reinforcement and will be pretreated with varying doses of either S(-)- or R(+)-nornicotine. In another experiment, rats will be pretreated repeatedly with either S(-)- or R(+)-nornicotine and tested for nicotine self-administration or sucrose-reinforced responding, thus assessing if effect of each nornicotine enantiomer is long-lasting or transient. The long-range goal of this preclinical work is to develop a novel medication for smoking cessation.